The present invention generally relates to a cylinder head construction and, more particularly, to a cylinder head construction for an internal combustion engine of DOHC (double-overhead-camshaft) type having a plurality of exhaust ports for each engine cylinder.
Numerous patent literatures including, for example, the U.S. Pat. No. 4,354,468, patented Oct. 19, 1982, disclose an automobile engine having a plurality of exhaust ports for each engine cylinder used for improving both the engine output characteristic and the exhaust efficiency.
As disclosed in, for example, the U.S. Pat. No. 4,267,811, patented May 19, 1981, the cylinder head used in this type of high power engine is of a construction having a plurality of exhaust ports each adapted to be communicated at one end with an associated combustion chamber and at the opposite end with an exhaust manifold, and also having at least exhaust port defining walls and a lower deck with a coolant flow passage defined therebetween.
As is well known to those skilled in the art, the automobile exhaust gases being a product of combustion evolve heat of highly elevated temperature. Accordingly, a portion of the prior art cylinder head between each neighboring exhaust ports is generally susceptible to thermal deformation under the influence of the very hot heat of the exhaust gases flowing through the exhaust ports.
The cylinder head is, when mounted on the mating cylinder block to complete an engine construction, tightly secured to the mating cylinder block by the use of a plurality of bolts. In general, the contact pressure exerted between the cylinder head and the cylinder block is relatively high at a location adjacent and around each bolt used to connect the cylinder head and block together, and it decreases progressively with increase in distance from the respective bolt. In particular, the contact pressure exerted between the cylinder head and the cylinder block is smaller at a portion of the cylinder head intermediate between the neighboring bolts than at the remaining portion thereof, and accordingly, even a slight thermal deformation occurring at that portion of the cylinder head is liable to result in the leakage of a portion of combustion gases from an eventually created gap between the cylinder head and the cylinder block.